1. Field of the Invention
The present invention is directed to a mechanism and method for reducing likelihood of fatigue failure in a high pressure fuel system. In particular, the present invention is directed to a specific juncture geometry that may be utilized in high pressure pump and/or common fuel rail systems.
2. Description of Related Art
With the advent of increased fuel economy and reduced emissions requirements imposed by the government, various fuel systems have been developed to precisely control the amount of fuel that is injected during the injection events of a combustion cycle. In particular, high pressure fuel injection systems have been developed which provide increased control of the fuel injected by the fuel injectors of an internal combustion engine in comparison to conventional fuel injection systems.
Such high pressure fuel injection systems typically utilize at least one high pressure pump that pressurizes the fuel to be injected by the fuel injectors. Fuel systems may utilize a plurality of such pressure pumps corresponding to the number of fuel injectors, each of the pumps providing highly pressurized fuel to a fuel injector. Other fuel systems utilize fewer high pressure pumps in conjunction with a high pressure common rail. In such implementations, one or more high pressure pumps are connected to the high pressure common rail to thereby provide highly pressurized fuel to the fuel injectors of the internal combustion engine. The common rail then distributes the pressurized fuel to each of the fuel injectors.
A limitation of such high pressure fuel injection systems briefly described above has been found in that the high pressures of the pressurized fuel, which in certain instances, reach up to 30,000 p.s.i. or higher, for example, can cause fatigue failure in the various components of the fuel injection system. In particular, the rapid stress cycling of the high pressure pump and/or the common rail at these high pressures can cause the fuel passages in the fuel injection system to fail due to fatigue. Such fatigue failure has been found to be especially pronounced in the junctures of the fuel passages in which the direction of the fuel flow is changed or otherwise distributed. For example, fatigue failure has been observed occurring near the junction for a branch connector in the common rail at which the passages for each of the injectors are connected to the common rail. A similar type of fatigue failure has also been observed in high pressure pumps and fuel passages that are associated therewith where the direction of the fuel is changed or otherwise distributed.
To address the above identified problems associated with high pressure fuel systems, a novel mechanism and method for reducing fatigue failure in a high pressure pump and common rail fuel system has been proposed in the art. For example, U.S. Pat. No. 5,979,945 issued to Hitachi et al. discloses a common rail including a pipe connecting arrangement including an intersection of a smaller diameter hole with a larger diameter hole, the geometry of the holes being configured using various different designs to improve the strength of the pipe connecting arrangement as well as resistance against internal pressure fatigue. The Hitachi et al. reference also discloses that in one geometry of the branch connector, the axes of the two holes are offset relative to each other so that the axes do not intersect.
Moreover, various materials, as well as materials treated in accordance with various treatment processes, have been found to be appropriate for use in fuel injection valve bodies. For example, Japanese Patent 2002-241922A issued to Yasusaka discloses a fuel injection valve body consisting of a high alloy steel containing 5 to 6% Cr, 1.0 to 1.3% Mo, and ≧0.1 V. The reference also discloses that the fuel injection valve body is treated by gas nitriding to thereby provide a strong and dense layer consisting of Fe3N, and a nitrided diffusion layer having a highly nitrided hardness. The reference notes that improvement in durability and pressure resistance can be obtained.
Despite the improvements in resisting fatigue failures as described by the Hitachi et al. reference, further improvements are desirable to further increase durability of high pressure fuel systems. In particular, a mechanism and method for improving fatigue failure resistance in a high pressure pump and/or common rail is desirable to further enhance the durability of high pressure fuel systems utilizing such components.